Grid-UMOSFET with electric field shielding of gate oxide

• US 8,946,726 B2
• Filed: 03/20/2013
• Issued: 02/03/2015
• Est. Priority Date: 09/14/2007
• Status: Active Grant

• Current Assignee: Wolfspeed, Inc.
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Harris, Christopher, Konstantinov, Andrei, Svederg, Jan-Olov
• Primary Examiner(s): Valentine, Jami M
• Application Number:
  US13/847,564
• Publication Number:
  US 20130270577A1
• Time in Patent Office: 685 Days
• Field of Search: 257/77, 438/33
• US Class Current: 257/77
• CPC Class Codes: H01L 29/0623 Buried supplementary region, e.g. buried guard ring multi-RESURF H01L29/0634
• CPC Class Codes: H01L 29/1095 Body region, i.e. base region, of DMOS transistors or IGBTs cell layout H01L29/0696
• CPC Class Codes: H01L 29/1608 Silicon carbide
• CPC Class Codes: H01L 29/2003 Nitride compounds
• CPC Class Codes: H01L 29/41741 for vertical or pseudo-vertical devices
• CPC Class Codes: H01L 29/41766 with at least part of the source or drain electrode having contact below the semiconductor surface, e.g. the source or drain electrode formed at least partially in a groove or with inclusions of conductor inside the semiconductor H01L29/41733 - H01L29/41758 take precedence
• CPC Class Codes: H01L 29/4238 characterised by the surface lay-out
• CPC Class Codes: H01L 29/45 Ohmic electrodes
• CPC Class Codes: H01L 29/66068 the devices being controllable only by the electric current supplied or the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched, e.g. three-terminal devices
• CPC Class Codes: H01L 29/66727 with a step of recessing the source electrode
• CPC Class Codes: H01L 29/66734 with a step of recessing the gate electrode, e.g. to form a trench gate electrode
• CPC Class Codes: H01L 29/7813 with trench gate electrode, e.g. UMOS transistors trench gate electrodes per se H01L29/4236
• CPC Class Codes: H01L 29/7827 Vertical transistors H01L29/7802, H01L29/78642 take precedence

Abstract

A trench metal oxide semiconductor field effect transistor or UMOSFET, includes a buried region that extends beneath the trench and beyond a corner of the trench. The buried region is tied to a source potential of the UMOSFET, and splits the potential realized across the structure. This effectively shields the electric field from the corners of the trench to reduce gate oxide stress, and resultantly improves device performance and reliability.

Claims

1. A semiconductor device comprising:

a drift layer of a first conductivity type;

a channel layer of a second conductivity type on the drift layer, the second conductivity type opposite the first conductivity type;

a source layer of the first conductivity type on the channel layer;

a source contact extending on the source layer;

a trench extending through the source layer and the channel layer, and into the drift layer, so that a bottom of the trench is within the drift layer;

a gate electrode within the trench;

a buried region of the second conductivity type within the drift layer, the buried region extending laterally to include a portion directly underneath the trench so that a shallow region of the drift layer is between the bottom of the trench and the buried region; and

a conductive via electrically connecting the source contact to the buried region.

2. The semiconductor device of claim 1, wherein the drift, channel and source layers are silicon carbide epitaxial layers.

3. The semiconductor device of claim 1, wherein the conductive via is of the second conductivity type and the source contact is embedded into an upper surface of the conductive via, and wherein the source contact embedded within the conductive via is surrounded by material of the second conductivity type and thereby separated from the source and channel layers.

4. The semiconductor device of claim 3, wherein the source contact is a metal.

5. The semiconductor device of claim 1, wherein the first conductivity type is n-type conductivity and the second conductivity type is p-type conductivity.

6. The semiconductor device of claim 1, comprising a plurality of additional conductive vias separated from each other and each electrically connecting the source contact to the buried region.

7. The semiconductor device of claim 1, wherein the buried region is an implanted region.

8. The semiconductor device of claim 1, wherein the gate electrode is comprised of polysilicon.

9. A grid U-shape Metal Oxide Semiconductor Field Effect Transmitter (UMOSFET) comprising:

a drift layer of a first conductivity type;

a channel layer of a second conductivity type on the drift layer, the second conductivity type opposite the first conductivity type;

a source layer of the first conductivity type on the channel layer;

a source contact having a plurality of source contact fingers extending on the source layer substantially parallel with respect to each other;

a plurality of trenches extending substantially parallel with respect to the plurality of source contact fingers, and through the source layer and the channel layer into the drift layer, so that bottoms of the plurality of trenches are within the drift layer;

a plurality of gate electrodes respectively within the plurality of trenches;

a plurality of buried regions of the second conductivity type within the drift layer, the plurality of buried regions respectively extending laterally to include a portion directly underneath the plurality of trenches so that shallow regions of the drift layer are between the bottoms of the plurality of trenches and the plurality of buried regions; and

conductive vias electrically connecting the plurality of source contact fingers to the plurality of buried regions.

10. The grid UMOSFET of claim 9, wherein the drift, channel and source layers are silicon carbide epitaxial layers.

11. The grid UMOSFET of claim 9, wherein the conductive vias are of the second conductivity type and the plurality of source contact fingers are embedded into an upper surface of respective ones of the conductive vias, and wherein the plurality of source contact fingers embedded within the conductive vias are surrounded by material of the second conductivity type and thereby separated from the source and channel layers by portions of the conductive vias.

12. The grid UMOSFET of claim 11, wherein the source contact is a metal.

13. The grid UMOSFET of claim 9, wherein the first conductivity type is n-type conductivity and the second conductivity type is p-type conductivity.

14. The grid UMOSFET of claim 9, wherein each respective one of the plurality of source contact fingers are electrically connected to the plurality of buried regions by a plurality of the conductive vias.

15. The grid UMOSFET of claim 9, wherein the plurality of buried regions are implanted regions.

16. The grid UMOSFET of claim 9, wherein the plurality of gate electrodes are comprised of polysilicon.

17. A semiconductor device comprising:

a plurality of semiconductor layers;

a trench Metal Oxide Semiconductor Field Effect Transistor (MOSFET) disposed within the plurality of semiconductor layers, the trench MOSFET comprising a trench for a gate contact;

a long channel Junction Field Effect Transistor (JFET) including a buried region within a lowermost layer of the plurality of semiconductor layers, the buried region extending laterally to include a portion directly underneath the trench of the trench MOSFET so that a shallow region of the lowermost layer is between the trench of the trench MOSFET and the buried region; and

the buried region of the long channel JFET is electrically coupled to a source potential applied to the trench MOSFET.

18. The semiconductor device of claim 17, wherein the plurality of semiconductor layers are silicon carbide epitaxial layers.

19. The semiconductor device of claim 17, further comprising:

a source contact;

a conductive via extending through the plurality of semiconductor layers, and electrically connecting the source contact and the buried region; and

a portion of the source contact is embedded within the conductive via, the embedded portion of the source contact is separated from the plurality of semiconductor layers by the conductive via.

20. A semiconductor device comprising:

a plurality of semiconductor layers;

a trench Metal Oxide Semiconductor Field Effect Transistor (MOSFET) disposed within the plurality of semiconductor layers, the trench MOSFET comprising a trench for a gate contact;

a buried region within a lowermost layer of the plurality of semiconductor layers, the buried region extending laterally to include a portion directly underneath the trench of the trench MOSFET so that a shallow region of the lowermost layer is between the trench of the trench MOSFET and the buried region; and

the buried region is electrically coupled to a source potential applied to the trench MOSFET.

21. The semiconductor device of claim 20, wherein the plurality of semiconductor layers are silicon carbide epitaxial layers.

22. The semiconductor device of claim 20, further comprising:

a source contact;

a conductive via electrically connecting the buried region to the source contact; and

a portion of the source contact is embedded within the conductive via, the embedded portion of the source contact is separated from the plurality of semiconductor layers by the conductive via.